Description: Polol S7V8A - step-up/step-down converter - 2,5-8V 1A.
The S7V8A inverter is a pulse voltage regulator of the step-up/step-down type (buck-boost). It converts the input voltage of 2.7 V - 11.8 V to an output value, adjustable by the user from the range: 2.8 V to 8 V with an average efficiency of 80%. This means that the input voltage can be lower, higher or equal to the input value, making the system functional and versatile. The flexibility of the input voltages makes the system ideal for battery-powered systems where stability of the supply voltage and its independence from the battery charge level is required.
Examples of application of the Polol converter
- Maintaining a stable voltage of 5 V in systems powered from a basket with four NiMh batteries (sticks), which when fully charged give a voltage of about 6 V, partiallydischarged below 5 V.
- The systems are powered by 3.3 V from a single Li-Po cell during the entire battery discharge cycle.
- Power supply for 5V systems from a 9-volt battery, which can give a voltage below the required 5V, partially discharged.
In standard application, the system allows for current draw up to 1A in step-down mode, i.e. when the supply voltage is higher than the desired output voltage. When the input voltage is lower than the output voltage (step-up mode), the current capacity of the converter decreases according to the graph in the figure below.
The graph shows the relationship between the maximum current capacity and the input voltage.
Use of the S7V8A inverter
The module has four outputs: VIN input voltage, VOUT output voltage, GND ground and SHDN pin switching the system into standby mode.
- VIN - input voltage from 2.7 V to 11.8 V. At lower voltage the controller will not start. Higher one may permanently damage the system.
- GND - ground potential.
- VOUT - output voltage, selectable with a potentiometer in the range of 2.5 V - 8.0 V.
- SHDN - low state (below 0.4 V) switches the system into low power consumption state. The current consumption in the sleep mode depends on the resistor (100k ohm) pulling SHDN to VIN and is 10 uA per volt. For example, when the VIN supply voltage is 5 V, the system will draw 50 uA. To permanently switch on the system, the voltage above 1.2 V must be applied to the SHDN pin, permanently connected to the VIN or left unconnected (the built-in pull-up resistor will trip).
Choice of output voltage in step-up/step-down converter
The voltage is set using a potentiometer. When using the meter, select a value from the permissible range of 2.5 V to 8 V. The potentiometer does not have a physical lock, which means that you can set a voltage higher or lower than the permissible voltage. However, this can lead to permanent damage to the system.
The output voltage can be approx. 3 % higher than the desired one when the system is operating without load. This value can also drop slightly when current consumption is close to the limits.
Efficiency of the Polol S7V8A inverter
Efficiency is defined as the ratio of input power to output power (Pout/Pin). This parameter is particularly important for battery operation when it is important to keep the system running as long as possible on a single charge. The efficiency of the inverter depends on the flowing current and the input voltage (graph below). On average, it is between 85 and 95 %, which allows the maximum use of battery power.
The efficiency of the controller for 3.3V output voltage.
Efficiency of the regulator for the output voltage of 5.0V.
Regulator efficiency for output voltage of 7.5V.
Voltage jumps (pins)
In electronic circuits the starting current may cause the occurrence of so-called pins, i.e. sudden voltage surges to a value above a set level. If the amplitude of the pins exceeds the permissible value of the regulator, it can be destroyed. Therefore, if the circuit will be supplied with voltage above 9 V or the load will have high inductance, we recommend solder a capacitor of 33 uF or higher as close to the circuit as possible between VIN and GND.
Polol S7V8A inverter specification
- Input voltage: 2.7 V to 11.8 V
- Maximum output current:
- 1 A (step-down)
- 0.5 A (step-up)
- Output voltage adjustable: 2.5 to 8 V
- Temperature protection
- Short circuit protection
- Dimensions: 17 x 11 x 3 mm
- Weight: 0.5 g (without connectors)