Description.

The circuit diagram shown here is of a 10V switching regulator based on the LM5007 from National Semiconductors. The LM5007 is an integrated step down switching regulator which has all necessary systems required for making a cost effective and reliable switching regulator circuit. The IC is available in MSOP-8, LLp-8 packages and has a lot of  built in  features like thermal shut down, under voltage lock out, duty cycle limiting, current limiting etc.

The output voltage of this regulator can be adjusted using the resistor R3 and R4. For the given values of R3 and R4 in the circuit diagram, the output voltage will be 10V. The equation governing the output voltage is Vout = 2.5 x (R3+R4)/R4. Resistor R1 sets the switch on time and C4 is the boost boot strap capacitor. Resistor R2 determines the variation of OFF time and C3 is a decoupling capacitor.

Circuit diagram.

Notes.

• The supply voltage can be anything between 12 to 72V DC.
• Output voltage can be adjusted using R3 and R4.
• C1  and C5 are polyester capacitors.
• C1 and C2 must be rated at least 100V.
• R5 and C5 forms a filter network.
• The output current limit of LM5007 is 700mA.

Description.
Here is the circuit diagram of a 30V/3A adjustable regulator using the LM723 IC from the National Semiconductors. LM723 is an integrated series regulator whose output voltage can be adjusted between 2V and 37V. The IC by itself can deliver an output current of 150mA and the maximum input voltage to the IC is 40V.
Here 3A output current is attained by adding a pass transistor (Q1) to the ICs output. The pass transistor used here is a Darlington transistor MJ3001. The internal reference voltage of the IC is 7.15V and it is available at pin6. POT R1 can be used to adjust the output voltage.
Circuit diagram.

Notes.

• Assemble the circuit on a good quality PCB.
• T1 can be a 230V primary, 25V secondary, 5A step down transformer.
• Q1 must be fitted on a proper heat sink.
• Output voltage can be adjusted by using the POT R1.

Description.
The circuit diagram shown here is of a simple DC power delay circuit that is based on an SCR. This circuit is a very handy one and can be employed in many applications. The working of this circuit is very simple. When the input power is applied the capacitor C2 charges through resistor R2 and when the voltage across the capacitor just exceeds the Zener diode D3’s breakdown voltage, it breaks down and the SCR H1 is triggered and the delayed power will be available at the delayed OUT terminal.
Circuit diagram.

Notes.

• The circuit must be assembled on a good quality PCB.
• The Zener diode must be rated half the input supply voltage.
• The current capacity of the circuit depends on the SCR and here it is 4A.

Description.
Here is the circuit diagram of a 12V boost converter using IC LM2698 from National Semiconductors. The LM2698 is a general purpose boost converter with an 18V, 1.35A. 0.2 Ohm internal switch. This results in high efficiency power conversion to outputs ranging from 2.2V to 17V DC. The input supply voltage range is 2.2V to 17V DC. The IC has excellent line and load regulation and frequency compensation over the entire input voltage range.

In the circuit diagram given here, the IC is wired to produce an output voltage of 12V from 5V input. The working of this circuit is as follows. Input voltage is fed to the analog power input (pin6) of the IC. During the first phase the internal switch is closed and the diode D1 is reverse biased. Energy will be stored in the inductor L1 and the load current is supplied by the capacitor C3. During second phase the internal switch will be closed and the diode D1 will be forward biased. Energy stored in the inductor L1 is transferred to the output capacitor C3 and the load. The switching frequency of the IC can be selected using the FSLCT (pin 7) of the IC. If pin 3 is connected to the supply voltage, the switching frequency will be 1.25 Mhz and if pin 3 is connected to the ground, switching frequency will be 600Khz. Resistors R2 and R3 forms the feedback network while R1 and C1 forms the compensation network. The input capacitor C2 prevents the impedance interactions of the circuit with the supply voltage source.
Circuit diagram.

Notes.

• Assemble the circuit on a good quality PCB.
• The input supply can be anything between 4.5 to 5.5V DC.
• Do not connect loads that consume more than 400mA.
• At 12V output , the IC can deliver only up to 400mA.
• C2 and C3 must be low ESR multi-layer ceramic capacitors.
• D1 can be a low forward drop Schottky diode (like 0MQ040N from Motorola).
• Pin 3 (SHDN) connected to the ground will shutdown the circuit.

Description.

Here is the circuit diagram of a 5V buck switching regulator based on the IC LM2678 from National Semiconductors. LM2678 series of regulators are monolithic integrated circuits which provide all necessary functions required for a buck switching regulator and can drive up to 5A loads. The IC has more than 90% efficiency and has excellent load and line regulation. The LM2678 is available in three fixed output voltages (3.3V, 5V, 12V) and an adjustable output version. The IC is also packed with a handful l of features like thermal shutdown, current limiting and ON/OFF control.

The circuit given here is based on the version LM2678-5.0 which gives an output of 5V.The input voltage for the regulator is fed to the pin 2 of the IC. Capacitors C1 to C4 are input bye-pass capacitors. They also provide current to the ICs control switch when it is switched ON first. Capacitor C5 boosts the gate drive of the internal MOSFET and makes it fully ON. This minimises switching loses and helps to attain high efficiency.Pin7 is the ON/OFF pin and the regulator will shut down if this pin is connected to the ground. Current drain during the shutdown mode will be less than 50uA.Schottky diode D1 is used as a freewheeling diode. When the control switch (internal MOSFET) is switched OFF the current from inductor L1 flows through this diode. Capacitors C6 and C7 and output filter capacitors.

Circuit diagram.

Notes

• Assemble the circuit on a good quality PCB.
• The power supply for the circuit can be anything between 8 to 40V DC.
• The feedback wiring must be placed as away as possible from the inductor L1.
• Do not use loads that consume more than 5A.
• A heat sink is seriously recommended for the IC.