Adopt the high-pressure power module design method of UC3901 control chip
In order to improve the reliability of the high-pressure power system, reduce the impact on low tension circuit of the high tension circuit, high-pressure and low tension circuit should isolate. The commonly used segregation method is: The power main circuit adopts the voltage transformer to isolate, feedback the controlling circuit and adopt light-coupled isolation. Such segregation design method is simple and reliable, the application area is wide. But in the high-reliability application (resists irradiates) Or isolate the requirement great (such as above 2500 V) Occasion,seem light-coupled isolation unable to do what one wishes, it feedback to isolate it last method by a controlling circuits getting more appropriate magnetism at this moment, design method of magnetism feedbacking, miniaturized high-pressure power module of UC3901 control chip that this text will introduce to adopt.
Function characteristic of 1 UC3901 control device
UC3901 is that the segregation which TI Company produces feedbacks the generator. Utilize UC3901 and to isolate the voltage transformer and commutate the smoothing circuit together, the magnetic isolation of controlling circuit feedbacks the function in the realization DC/ DC power that can be very convenient. Mainly there are voltage reference, amplifier circuit, resonator, modulator circuit of range, export the driving circuit within UC3901. The job voltage range of UC390l can reach 4.5 V- 40 V, is lower than 4 in working voltage. At the 5 V, the output of the device is occluded, so can prevent the fault-operation. This device can be regarded as the reference signal of the amplifier directly. Because of this chip self-carrying resonator, so, needn’t the extra resonator to realize the output of the amplitude-modulated signal while working, this self-carrying resonator can also realize moving ahead simultaneously with the oscillating beacon of the external circuit conveniently while needing, thus meet the special requirement in the system. Modulate amplitude in the electric current fan-out capability with 15 mA of Ausgang of the circuit, it is 700& mu to suck electric current ability; A, if expand and suck electric current ability, can also connect the resistance of flow extending.
The designing requirements of 2 magnetic isolation reaction type high tension supplies
This text provides and adopts UC3901 magnetic isolation feedback controller to carry on the design method of the small-scale high tension supply, the designing requirement of this power is as follows: Input voltage (V) : 20- 32; Nominal voltage (V) : 22; Output voltage (V) : 300± 10; Output current (mA) Less than or equal to 20; Ripple (mV) : Less than or equal to 1500; Efficiency (& eta) : Greater than or equal to 75%; Voltage control degree (V) : Less than or equal to 2; Load regulation degree (V) : Less than or equal to 5; It is less than or equal to 10% to export the voltage overshoot; The output voltage delays being less than or equal to 30ms.
3 circuit design
The magnetic isolation feedbacked the principle of the high tension supply, it was LC passive smoothing circuit that input the smoothing circuit and adopted, what the inverter of power is adopted is that the inverter of push pull is isolated and designed with the power voltage transformer, it was voltage doubling rectifying circuit that was exported and is commutated and is adopted, it is capacitor filtering that is exported and filtered and is adopted, can join LC two-shot filtering if necessary, the magnetic isolation feedbacked the controlling circuit to adopt the controlling circuit (UC3901) of magnetic isolation , magnetic isolation voltage transformer and commutating the smoothing circuit to make up, PWM push pull controlling circuit adopts UC3525 to design.
3.1 PWM circuit design
PWM top management chip of this high tension supply adopts the control chip UC3525 of push pull, a foot of this chip connects the feedback control signal, inside is the reverse input end to compare the amplifier, 2 is the positively input end to compare the amplifier within the foot, the outside sets up the comparative voltage of basic reference of the amplifier through the resistance R19, R4, the value of this voltage should be less than the maximum value of the feedback control signal, because the turns ratio that magnetic isolation feedbacks the voltage transformer in this design is 1: 1,The maximum value of the feedback control signal is 2 V, so the voltage of 2 feet is set up as 1. 8 V. C4, R5 shake electric capacity and timing resistor separately, they have determined the operating frequency of UC3525, R15, C10 compare the FB network of the amplifier, 11 feet and 14 feet are PWM signal Ausgangs, receive the grids of two VMOS tubes of the main circuit separately through two pieces of resistance R5, R7, the values of R5, R7 can be several, usually used for reducing the grid to shake.
3.2 The magnetism, against circuit design
The magnetism can feedback the isolating circuit by the magnetic feedback controller UC3901, isolate the voltage transformer T2 sum signal to commutate the smoothing circuit (V2, C5, R9) Composition.
10 feet of UC390l are the same direction input end of the internal amplifier, can follow 1.5 V reference signal directly, 11 feet are the reverse input end of the internal amplifier, receive the feedback signal of the output voltage, C12, R15 are FB networks of the amplifier, can confirm the parameter through the test, C13, R16 shake the electric capacity and resistance.
3.3 Rectifying circuit
That outputted the rectifying circuit and adopted is that voltage doubling commutates the way. In the little output power occasion of high pressure, this is a kind of more practical circuit form, so can reduce the turns ratio of the voltage transformer, the withstand voltage of reducing the rectifier tube is required.
This text provides and adopts UC3901 to design the magnetism to feedback the method to isolate DC/ DC, the high tension supply which adopts the above-mentioned circuit design has good static behavior and dynamic characteristic, magnetism of this method it feedbacks principles to be the superposition of signal of feedback control in exchanging the pulse signal, then transmit alternate current signal to the primary side through isolating the voltage transformer and reuse the demodulation circuit of range and take the signal amplitude out, the impulse width that in order to be used for controlling PWM to output, realize the function of loop-locked voltage regulation. This principle is to adopt other methods to realize the magnetism feedback isolated design philosophy too.
Tags: control device, the generator, TI, Voltage transformer
