Negative voltage generating circuit

A negative voltage generating circuit includes a pulse generator U1, a switch, a resistor, a first capacitor, a first diode, a second diode, and a second capacitor. The pulse generator includes a positive voltage input pin coupled to a power supply, an oscillating output pin, and a negative voltage input pin. The switch includes a first terminal coupled to the oscillating output pin, a second terminal coupled to one terminal of the first capacitor, and coupled to the power supply via the resistor, and a third terminal being grounded. Another terminal of the first capacitor is coupled to the anode of the fist diode and the cathode of the second diode. The cathode of the first diode is grounded. The anode of the second diode is coupled to the positive voltage input pin of the pulse generator, and is coupled to ground via the second capacitor.

BACKGROUND

1. Field of the Invention

The present invention relates to a negative voltage generating circuit.

2. Description of Related Art

With rapid development of electronic technology, more and more electronic systems need both positive and negative voltages to operate, for example, operational amplifiers and computer PCI (Peripheral Component Interconnect) cards require negative voltage to operate.

What is desired, therefore, is to provide a simple low-cost negative voltage generating circuit for providing a negative voltage.

SUMMARY

An exemplary negative voltage generating circuit includes a pulse generator U1alternately outputting a high level signal and a low level signal, a switch, a resistor, a first capacitor, a first diode, a second diode, and a second capacitor. The pulse generator includes a positive voltage input pin, an oscillating output pin, and a negative voltage input pin. The switch includes a first terminal, a second terminal, and a third terminal. The positive voltage input pin is coupled to a power supply. The first terminal of the switch is coupled to the oscillating output pin. The second terminal of the switch is coupled to one terminal of the first capacitor, and is coupled to the power supply via the resistor. The third terminal of the switch is grounded. Another terminal of the first capacitor is coupled to the anode of the fist diode and the cathode of the second diode. The cathode of the first diode is grounded. The anode of the second diode is coupled to the positive voltage input pin of the pulse generator, and is coupled to ground via the second capacitor.

DETAILED DESCRIPTION

Referring to the drawing, a negative voltage generating circuit in accordance with an embodiment of the present invention includes a pulse generator U1alternately outputting a high level signal and a low level signal, a display unit U2, two resistors R1, R2, a MOSFET Q1, four capacitors C1˜C4, and two diodes D1, D2.

The pulse generator U1includes a positive voltage input pin V+, a first oscillating output pin osc1, a second oscillating output pin osc2, a third oscillating output pin osc3, a negative voltage input pin V−, and a plurality of data output pins p1˜p16. The positive voltage input pin V+ is coupled to a power supply Vcc, the second oscillating output pin osc2is coupled to the first oscillating output pin osc1via the resistor R1, the plurality of data output pins p1˜p16is electrically coupled to the display unit U2via a plurality of transmission lines. The gate of the MOSFET Q1is coupled to the third oscillating output pin osc3of the pulse generator U1. The source of the MOSFET Q1is coupled to one terminal of the capacitor C2, and is coupled to the power supply Vcc via the resistor R2. The drain of the MOSFET Q1is grounded. Another terminal of the capacitor C2is coupled to the anode of the diode D1and the cathode of the diode D2. The cathode of the diode D1is grounded. The anode of the diode D2is coupled to the negative voltage input pin V− of the pulse generator U1, and is coupled to ground via the capacitors C3, C4connected in parallel.

In this embodiment, the MOSFET Q1is a P-channel MOSFET. The diode D1is a Schottky diode. The pulse generator U1is an ICL7107 type A/D converter produced by INTERSIL Corporation in USA. The display unit U2is a digital display panel including a plurality of LED digital tube.

In use, the third oscillating output pin osc3of the pulse generator U1alternately outputs a high level and a low level pulse signal. When the third oscillating output pin osc3outputs a high level signal, the MOSFET Q1turns off, and the power supply Vcc charges the capacitor C2. When the capacitor C2is fully charged, no current passes through the resistor R2, the diode D1has a voltage drop (such as 0.2 V), thereby; the full voltage of the capacitor C2equals the difference between the voltage of the power supply Vcc and the voltage of the diode D1.

When the third oscillating output pin osc3outputs a low level signal, the MOSFET Q1turns on, the source of the MOSFET Q1outputs a low level signal, therefore, the voltage of the one terminal of the capacitor C2is 0V, and a voltage of the another terminal of the capacitor C2is negative. So the capacitor C2discharges through the capacitors C3, C4, and the diode D2, and the negative voltage input pin V− receives a negative voltage from the anode of the diode D2.

When the third oscillating output pin osc3outputs high level and low level signals alternately, the capacitor C2charges and discharges continuously. When the third oscillating output pin osc3outputs a low level signal, the capacitor C2discharges through the capacitors C3, C4, and the diode D2, at the same time, the capacitors C3and C4are charged. When the third oscillating output pin osc3outputs a high level signal, the capacitor C2is charged, at the same time, the capacitors C3and C4discharge through the diode D1, the negative voltage input pin V− stably and continuously receives a negative voltage from the anode of the diode D2.

For example, when the third oscillating output pin osc3outputs a high level signal, the capacitor C2is charged, and the full voltage of the capacitor C2equals the difference between the power supply Vcc and the voltage of the diode D1. When the third oscillating output pin osc3outputs a low level signal, a voltage of the one terminal of the capacitor C2is 0V, and a voltage of the another terminal of the capacitor C2is negative, the capacitor C2discharges through the capacitors C3, C4, and the diode D2, the negative voltage input pin V− receives a negative voltage from the anode of the diode D2, the value of the negative voltage equals the difference between the voltage of the capacitor C2and the voltage of the diode D2. The display unit U2is configured for displaying value of the negative voltage received at the negative voltage input pin V− of the pulse generator U1.

Because the negative voltage generating circuit can comprise one or more diodes connected between the another terminal of the capacitor C2and ground, which essentially forms a voltage dividing circuit, voltage received at the negative voltage input pin V− of the pulse generator U1can be selected according to the value and number of diodes used therein, The negative voltage generating circuit is simple, and low-cost.