Bipolar transistor adjustable shunt regulator circuit
An adjustable shunt regulator circuit has two current paths in parallel, with each current path having a bipolar transistor therein with the bases of the bipolar transistors of the two current paths connected in common. One of the current paths has a high impedance node. A MOS transistor has a gate connected to the high impedance node, and a source and a drain. A resistor divide circuit is connected in parallel to the source and drain of the MOS transistor and provides the output of the regulator circuit. The resistor divide circuit has a first resistor connected in series with a second resistor at a first node. A feedback connects the first node to the bases of the bipolar transistors connected in common of the two current paths.
1. An adjustable shunt regulator circuit comprising:
two current paths in parallel, the first path comprising a first MOS transistor coupled to a collector of a first bipolar transistor and a first resistor comprising a first end and second end wherein the first end is coupled to an emitter of the first bipolar transistor, and the second path comprising a second MOS transistor coupled to a collector of a second bipolar transistor, wherein a base of the first bipolar transistor and a base of the second bipolar transistor are connected in common;
a third MOS transistor comprising a source, a drain, and a gate, the gate connected to the collector of the second bipolar transistor;
a resistor divide circuit connected in parallel to the source and the drain of the third MOS transistor and providing an output of the regulator circuit; said resistor divide circuit having a second resistor comprising a first end and second end and a third resistor comprising a first end and a second end, wherein the first end of the second resistor is connected to the source of the third MOS transistor, the second end of the third resistor is connected to the drain of the third MOS transistor and the second end of the second resistor is connected to the first end of the third resistor to form a first node;
a fourth resistor having a first end connected to the second end of the first resistor and to an emitter of the second bipolar transistor and a second end connected to the third resistor; and
a feedback connection from the first node to the bases of the first bipolar transistor and second bipolar transistor.
2. The regulator circuit of claim 1 wherein the first bipolar transistor is an NPN transistor, the second bipolar transistor is an NPN transistor, and the third MOS transistor is a PMOS transistor.
3. The regulator circuit of claim 1 wherein the first bipolar transistor is a PNP transistor, the second bipolar transistor is a PNP transistor and the third MOS transistor is a NMOS transistor.
4. The regulator circuit of claim 1 , wherein the emitter of the first bipolar transistor is approximately ten times larger than the emitter of the second bipolar transistor.
5. The regulator circuit of claim 1 , wherein the regulator circuit does not contain an error amplifier.