Active peak voltage-limiting clamp circuit

1. An active peak voltage-limiting clamp circuit, electrically coupled to a power supply's transformer circuit which comprises a transformer for power conversion, a pulse modulation unit driving said transformer and generating a clock signal, and an output feedback unit electrically coupled to said transformer and said pulse modulation unit, wherein said active peak voltage-limiting clamp circuit is used to control the current of said transformer and comprises:

a signal acquisition unit electrically coupled to the primary side of said transformer to acquire and output an acquisition signal, said signal acquisition unit utilizing an auxiliary coil, which is installed beside said transformer, to obtain said acquisition signal, which is a proportional magnification or minification of the current of said transformer, said signal acquisition unit including a peak-to-peak detection unit to decide the maximum and the minimum of said acquisition signal;

a zero-point decision unit electrically coupled to said signal acquisition unit and receiving said acquisition signal and deciding a plurality of critical points of the periodical variation of said acquisition signal according to the maximum and minimum values of said acquisition signal;

a feedback unit electrically coupled to said signal acquisition unit and receiving said acquisition signal and generating a first feedback current according to said acquisition signal, wherein a second feedback current is obtained via shunting the current of the primary side of said transformer, and said first feedback current and said second feedback current are combined into a third feedback current;

a primary switch unit and a secondary switch unit electrically coupled to said transformer and controlling the current path of said transformer, wherein said pulse modulation unit determines the turn-on timing of said primary switch unit; and

a pulse control unit triggered by said third feedback signal, said clock signal and said critical points defined by said zero-point decision unit to control the turn-on and turn-off of said secondary switch unit and separate the operation of said secondary switch unit from that of said primary switch unit to form the excitation current periods of said transformer.

2. The active peak voltage-limiting clamp circuit according to claim 1 , wherein said signal acquisition unit utilizes a semiconductor element to proportionally magnify or minify the coil voltage and obtain said acquisition signal.

3. The active peak voltage-limiting clamp circuit according to claim 1 , wherein the excitation current period of said transformer has a positive semiperiod and a negative semiperiod, and the current increases at the rate of a given slope in said positive semiperiod, and the current decreases at the rate of another given slope in said negative semiperiod.

4. The active peak voltage-limiting clamp circuit according to claim 1 , wherein said zero-point decision unit is coupled to two ends of said auxiliary coil via a semiconductor element; when the current varies, said acquisition signal can thus turn on or turn off said semiconductor element to detect a plurality of critical points of the periodical variation of the excitation current of said transformer.

5. The active peak voltage-limiting clamp circuit according to claim 1 , wherein said pulse control unit has a minimum voltage limit; when the output voltage is lower than said minimum voltage limit because the no-load state makes the negative semiperiod of the excitation current period over extend, said negative semiperiod stops extending.

6. The active peak voltage-limiting clamp circuit according to claim 1 , wherein said pulse control unit utilizes a Zener diode to generate a minimum voltage limit.

7. The active peak voltage-limiting clamp circuit according to claim 1 , wherein said clock signal generated by said pulse modulation unit is a maximum period limit for the turn-on period of said secondary switch unit.

8. The active peak voltage-limiting clamp circuit according to claim 7 , wherein said secondary switch unit is turned off by the positive edge of said clock signal generated by said pulse modulation unit.

9. The active peak voltage-limiting clamp circuit according to claim 1 , wherein said feedback unit utilizes a voltage-controlled current source to generate a current inversely proportional to said acquisition signal.